You can now download any version of iOS for any iOS device, right from your Mac OSX desktop.
ipswDownloader lets you download all the iOS versions (iOS 1.x to iOS 4.x) for All iOS devices Apple TV, iPod Touch 1g, 2g, 3g,4g, iPhone 2g, iPhone 3g, iPhone 4, iPhone 4 CDMA, iPad, iPad 2, with a single click.
This makes downloading iOS pretty handy for jailbreaking and unlocking, whenever you need them for any of the iDevices. The app loads list of devices and iOS versions from server on startup, so you always have the latest iOS version available for each of the devices.
The app supports Growl notifications for downloads, and was able to deliver good download speeds of upto 6mbps on my 8mbps connection, certainly not a bad deal for a free service.